1. Field of the Invention
The invention relates to a method for driving a plasma display panel (PDP) of a surface discharge type of a matrix display system.
2. Related Background Art
In recent years, a practical use of a plasma display panel (PDP) is expected as a color display device of a large size and a thin type.
In the PDP, as is well known, electrode groups which mutually intersect are provided on the inside of a pair of substrates arranged so as to face each other through a discharge space and discharge cells are constructed at intersecting portions of the electrodes, and are selectively allowed to emit the light.
In a surface discharge type AC-PDP, for example, a plurality of maintaining electrode groups extending mutually in parallel are formed on the inner surface of the substrate on the display surface side and a dielectric layer and an MgO (magnesium oxide) layer are sequentially formed on the maintaining electrodes. Address electrodes are formed in parallel on the substrate on the back side so as to intersect the maintaining electrode pairs, a fluorescent material is formed on the address electrodes, and ribs are formed between the address electrodes. A mixture rare gas is filled in the discharge space.
The PDP operation is performed in a manner such that, for example, a predetermined voltage is first applied across the pair of maintaining electrodes, a discharge is started, a selection erasing pulse is subsequently applied to the address electrodes corresponding to discharge cells that are unnecessary for display, and wall charges in the dielectric layer are erased, thereby stopping the discharge.
Subsequently, a maintaining pulse lower than a discharge start voltage is applied to the maintaining electrode pair and the discharge is maintained with respect to the discharge cell corresponding to a display pixel. The fluorescent layer is excited by ultraviolet rays generated by the above operation and emits light. The MgO layer has functions for raising a secondary electron emission ratio and decreasing the discharge start voltage. By properly selecting a period of the maintaining pulse to maintain the discharge, a luminance of the display is adjusted.
In the surface discharge type AC-PDP, a scanning line is constructed by a set of (two) electrode lines and an alternating voltage is applied between the electrode lines, thereby forming a discharge. In this instance, the voltage is applied across the adjacent scanning lines so that polarities of the closest electrode lines are opposite because of a selectivity of the pixel.
In the AC-PDP of the surface discharge type, since transparent electrodes are used as maintaining electrodes, a resistivity is large. Hitherto, therefore, bus electrodes made of metal electrodes are further laminated in order to compensate a conductivity of the maintaining electrodes, thereby reducing a wiring resistance.
When the PDP is increases in size, however, since a wiring length of the metal electrode is long, the wiring resistance of the bus electrode itself cannot be also ignored.
In order to reduce the wiring resistance, it is considered that a width of the metal electrode is widened or a film thickness thereof is thickened. In the former case, since a ratio of shutting off the light emission in a unit light emitting region (discharge cell) increases, the luminance decreases. As the discharge cell size further decreases, its influence is conspicuous. In the latter case, since a film forming time becomes long, processing costs increase and, further, there is a limitation when the film is thickened by forming the film by an evaporation deposition.
In the AC-PDP, a current flowing in each discharge cell is not constant with respect to the time and is maximum in, for example, about hundreds of nanoseconds after the voltage pulse has been applied. After that, the current hardly flows in about hundreds of nanoseconds. In the maintaining discharge for the display (sustain discharge), since a pulse interval is equal to about a few microseconds, all of the discharge cells on one maintaining electrode pair (sustain line) are almost simultaneously discharged and currents almost simultaneously flow in all of the discharge cells.
The maximum value of the current of one maintaining electrode pair, therefore, is equal to a value added with the maximum value of the current flowing in each cell. A large current instantaneously flows in one maintaining electrode pair. The large instantaneous current causes a large voltage drop by a wiring resistance of the maintaining electrode, thereby deteriorating display characteristics.
As mentioned above, as a peak value of the discharge current is large, loads of a driving circuit and a power source of the AC-PDP increase and it is difficult to realize the large size of the PDP.